Use page type instead of tags for CSSSyntax macro

[wbamberg]

Summary

Use page-type instead of tags for the CSSSyntax macro.

We recently defined and added page types for pages under Web/CSS: mdn/content#15540 .

One of the purposes of this was to replace tags for describing the type of thing a page documented. @teoli2003 observed that it would be a good idea to start using page types as soon as possible, as this gives us an incentive to keep them maintained.

So this PR updates the CSSSyntax macro to use page types instead of tags.

Screenshots

UI should look exactly the same, except in places where tags and page-type don't agree, in which case page-type should be more accurate.

How did you test this change?

Ran yarn dev, looked at some Web/CSS pages. Really what we are testing is that the macro can figure out how to get the formal syntax from webref for each of the four kinds of thing: CSS shorthand properties, CSS properties, CSS types, CSS functions.

Shorthand properties

http://localhost:3000/en-US/docs/Web/CSS/border#formal_syntax
http://localhost:3000/en-US/docs/Web/CSS/grid#formal_syntax

Properties

http://localhost:3000/en-US/docs/Web/CSS/justify-content#formal_syntax
http://localhost:3000/en-US/docs/Web/CSS/margin-top#formal_syntax
http://localhost:3000/en-US/docs/Web/CSS/mask-clip#formal_syntax
http://localhost:3000/en-US/docs/Web/CSS/opacity#formal_syntax

Types

http://localhost:3000/en-US/docs/Web/CSS/color_value#formal_syntax
http://localhost:3000/en-US/docs/Web/CSS/gradient#formal_syntax

Functions

http://localhost:3000/en-US/docs/Web/CSS/clamp#formal_syntax
http://localhost:3000/en-US/docs/Web/CSS/min#formal_syntax
http://localhost:3000/en-US/docs/Web/CSS/max#formal_syntax
http://localhost:3000/en-US/docs/Web/CSS/transform-function/translateY#formal_syntax

[teoli2003]

I'm really excited about this!

And I find the code of the macro much more readable!

(We may be able to remove Tags and simplifies the platform very soon!)

[fiji-flo]

💯 great!

[wbamberg]

Thanks @fiji-flo ! Can we merge this, then?

[wbamberg]

I'm merging this, because it has ticks and I'd like to write another PR to add support for at-rule formal syntax, given #4656 (comment).